1. Field of the Invention
The present invention relates to a vibrating gyroscope, and more particularly to a vibrating gyroscope used in a video camera or the like to detect external vibrations such as hand shaking by detecting a rotational angular velocity and cancel out the vibrations on the basis of the detected information. The invention also relates to a method for adjusting the above type of vibrating gyroscope.
2. Description of the Related Art
FIG. 9 shows one example of the vibrating gyroscopes disclosed in Japanese Laid-Open Patent Publication No. 7-332988. This gyroscope is explained hereinbelow with reference to the drawings.
Referring to FIG. 9, a vibrating gyroscope 100 includes a vibrator 101. The vibrator 101 has a vibrating member 102. The vibrating member 102 is integrally formed by stacking a first piezoelectric substrate 103 and a second piezoelectric substrate 104 with an intermediate electrode 105 therebetween. Two divided electrodes 106a and 106b are formed on the main surface of the first piezoelectric substrate 103 in the longitudinal direction of the first piezoelectric substrate 103 in such a manner that they are separated from each other. A common electrode 107 is disposed on the entire main surface of the second piezoelectric substrate 104.
The common electrode 107 serves as a driving electrode for vibrating the vibrator 101, while the divided electrodes 106a and 106b serve as detecting electrodes.
In the vibrating gyroscope 100 constructed as described above, the vibrator 101 vibrates under a bending mode in the direction orthogonal to the main surfaces of the first piezoelectric substrate 103 and the second piezoelectric substrate 104 (hereinafter referred to as "the driving direction DX"). An application of the rotational angular velocity .omega. around the center axis O of the vibrator 101 causes a Coriolis force in the direction orthogonal to the driving direction DX (hereinafter referred to as "the detecting direction DY").
It is known that the sensitivity of gyroscopes generally becomes the highest when the resonant frequency in the driving direction substantially coincides with the resonant frequency in the detecting direction. The common method to achieve the above is to remove a portion of the vibrating member, as disclosed in Japanese Laid-Open Patent Publication Nos. 2-298812 and 9-178487.
For example, referring to FIG. 9 in the Japanese Laid-Open Patent Publication No. 9-178487, a lateral portion S1 of the first piezoelectric substrate 103 and a lateral portion S2 of the second piezoelectric substrate 104 are removed to shift (lower) the resonant frequency in the detecting direction DY, whereby the resonant frequency fx in the driving direction DX is caused to match the resonant frequency fy in the detecting direction DY in the vibrating gyroscope 100.
However, the above known type of vibrating gyroscope and the adjusting method therefor present the following problems.
More specifically, in the vibrating gyroscope 100, the resonant frequency fx in the driving direction DX is unstable. This is because the resonance point in the driving direction DX is split causing discrete oscillation frequencies. The vibration of the vibrator thus becomes unstable, and the S/N ratio of the vibrating gyroscope is degraded.
Accordingly, the resonant frequency fx in the driving direction DX is so unstable that the sensitivity is decreased or deviated when the resonant frequency fx in the driving direction DX coincides with the resonant frequency fy in the detecting direction DY. As a result, a stable signal resulting from the Coriolis force cannot be obtained.
In particular, if the resonant frequency fx in the driving direction DX matches the resonant frequency fy in the detecting direction DY merely by shifting the resonant frequency fy, the resonant frequency fx in the driving direction DX is not changed at all. This method, therefore, cannot solve the above-described problems.
Also, in the conventional gyroscope, since the resonant frequency fx in the driving direction DX substantially matches the resonant frequency fy in the detecting direction DY, the Q factor in the detecting direction is higher. Accordingly, in this vibrating gyroscope 100, there is a great phase delay in the detection signal, thus causing low output response characteristics.
In regard to the method for etching the lateral surface of the vibrator 101, the base on which the vibrator 101 is mounted is not considered at all. In practice, the lateral surface is difficult to etch depending on the shape of the base.